1. Field of the Invention
The present invention relates to a battery pack accommodating unit cells.
2. Description of the Related Art
A battery pack is installed, for example, on a vehicle. A battery pack 50 according to a first conventional example is illustrated in FIGS. 1A and 1B. The battery pack 50 according to the first conventional example includes a power supply 52 including unit cells 51, a service plug connector 54 including a pair of shutoff terminals 53 of the power supply 52, a pair of output terminals 55 of the power supply 52, and a case 56 accommodating the power supply 52. Each of the output terminals 55 is in a form of a terminal for tightening a bolt. The output terminals 55 are connected to power supply terminals 70 on the vehicle side by bolt-tightening.
A service plug grip 57 is attached to the service plug connector 54. Detaching the service plug grip 57 can shut off the power supply 52.
A battery pack 60 according to a second conventional example is illustrated in FIGS. 2A and 2B. The battery pack 60 according to the second conventional example includes a power supply 62 including unit cells 61, a service plug connector 64 including a pair of output terminals 63 of the power supply 62, a pair of output connectors 66 each including one of a pair of output terminals 65 of the power supply 62, and a case 67 accommodating the power supply 62. The output connectors 66 are connected to a pair of connectors 73 each including one of a pair of power supply terminals 72 on the vehicle side. This connecting connects the output terminals 65 with the power supply terminals 72.
A service plug grip 68 is attached to the service plug connector 64. Detaching the service plug grip 68 can shut off the power supply 62.
However, according to the first and second conventional examples, no attention is paid to adding the respective battery packs 50, 60.
On the other hand, for coping with request for increased battery capacity and the like, a battery module capable of adding the battery packs is conventionally proposed (refer to JP 2008-066093 A). As illustrated in FIGS. 3, 4A and 4B, a battery module 80 according to a third conventional example is constructed with two types of battery packs, that is, a main battery pack 81 and sub-battery packs 90. The main battery pack 81 includes a power supply 83 including unit cells 82, a pair of output terminals 84 of the power supply 83, and additional terminals 85 used for adding other battery packs to the power supply 83. The power supply 83 is accommodated in a case 86. On both side face sides of the case 86, there are provided recessed outer wall portions 86a. Each of additional terminals 85 is provided on a surface of each of the concave outer wall portions 86a. 
The sub-battery pack 90 includes an additional power supply 92 including unit cells 91 and additional terminals (output terminals) 93 of the additional power supply 92. The additional power supply 92 is accommodated in a case 94. Protruding outer wall portions 94a are provided on one side face side of the case 94, and recessed outer wall portions 94b are provided on the other side face side of the case 94, respectively. Each of additional terminals 93 is provided at each of the protruding outer wall portions 94a and each of the recessed outer wall portions 94b. 
Mating the protruding outer wall portions 94a of the sub-battery pack 90 with the recessed outer wall portions 86a of the main battery pack 81, the additional terminals 85 of the main battery pack 81 are connected to the additional terminals 93 of the sub-battery pack 90. Further, mating the protruding outer wall portion 94a of the other sub-battery pack 90 with the recessed outer wall portion 94b of the sub-battery pack 90, the additional terminals 93 of the sub-battery pack 90 is connected to the additional terminals 93 of the other sub-battery pack 90. The above operations can add the sub-battery packs 90 in the battery module 80.